[PATCH] ftrace: do not call ftrace_special() from down().

[Pekka Paalanen]

The moment mmiotrace is enabled, I hit a NULL deref in:

IP: [<ffffffff80256e71>] __trace_special+0x17c/0x23a
Call Trace:
 [<ffffffff802573cc>] ftrace_special+0x6f/0x9a
 [<ffffffff8023e3e4>] down+0x19/0x4a
 [<ffffffff80228adc>] acquire_console_sem+0x42/0x58
 [<ffffffff8035d273>] con_flush_chars+0x28/0x43
 [<ffffffff80354a70>] write_chan+0x22e/0x334
 [<ffffffff802244e9>] ? default_wake_function+0x0/0xf
 [<ffffffff8035236d>] tty_write+0x195/0x228
 [<ffffffff80354842>] ? write_chan+0x0/0x334
 [<ffffffff8027c23a>] vfs_write+0xae/0x137
 [<ffffffff8027c6e3>] sys_write+0x47/0x70
 [<ffffffff8020b1db>] system_call_after_swapgs+0x7b/0x80

which means 'entry' in __trace_special() is NULL.

Signed-off-by: Pekka Paalanen <pq@xxxxxx>
---
 kernel/semaphore.c |    1 -
 1 files changed, 0 insertions(+), 1 deletions(-)

diff --git a/kernel/semaphore.c b/kernel/semaphore.c
index bbab232..62f30c2 100644
--- a/kernel/semaphore.c
+++ b/kernel/semaphore.c
@@ -54,7 +54,6 @@ void down(struct semaphore *sem)
 {
 	unsigned long flags;
 
-	ftrace_special(sem->count, 0, __LINE__);
 	spin_lock_irqsave(&sem->lock, flags);
 	if (likely(sem->count > 0))
 		sem->count--;
-- 
1.5.4.5

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